Field
Implementations of the present disclosure generally relate to an apparatus and method for uniform sputter deposition of materials into the bottom and sidewalls of high aspect ratio features on a substrate.
Description of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technology challenges for next generation very large-scale integration (VLSI) and ultra large-scale integration (ULSI) of semiconductor devices. However, as the miniaturization of circuit technology continues, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on processing capabilities. For example, as circuit densities increase for next generation devices, the widths of interconnects, such as vias, trenches, contacts, gate structures and other features, as well as the dielectric materials therebetween, decrease while the thickness of the dielectric layers remains substantially constant, with the result of increasing the aspect ratios of the features.
Sputtering, also known as physical vapor deposition (PVD) is widely used to deposit metallic features in integrated circuits. Sputtering is used to deposit layers for use as diffusion barriers, seed layers, primary conductors, antireflection coatings, and etch stops. A source material, such as a target, is bombarded by ions strongly accelerated by an electric field. The bombardment ejects material from the target and the material then deposits on the substrate. During deposition, ejected particles may travel in varying directions, rather than generally orthogonal to the substrate surface, resulting in overhanging structures formed on corners of high aspect ratio features in the substrate. Overhang may undesirably result in holes or voids formed within the deposited material, resulting in diminished electrical conductivity of the formed feature. Higher aspect ratio geometries have a higher degree of difficulty to fill without voids.
One technique developed to allow the use of sputtering to deposit thin films in the bottom of a high aspect ratio feature is collimator sputtering. A collimator is a filtering plate positioned between a sputtering source and a substrate. The collimator typically has a uniform thickness and includes a number of passages formed through the thickness. Sputtered material passes through the collimator on its path from the sputtering source to the substrate. The collimator filters out or collects material that would otherwise strike the workpiece at acute angles exceeding a desired angle.
The actual amount of material filtering accomplished by a given collimator depends on the aspect ratio of the apertures through the collimator. Material such as particles traveling on a path approaching normal to the substrate pass through the collimator and are deposited on the substrate. This allows improved coverage in the bottom of high aspect ratio features. However, certain problems exist with the use of prior art collimators, which typically have an overall hexagonal shape. Unfortunately, PVD chambers with prior art collimators often suffer from cell clogging and leave a six-point deposition near an edge of the substrate due to shadowing of the corners of the hexagonal collimator.
Therefore, a need exists for improvements in the uniformity of depositing source materials across a substrate by PVD techniques.